1. Field of the Invention
This invention relates to a surgical method and analgesic compositions for use in surgery. A composition of the present invention is applied during surgery to reduce pain.
2. Brief Description of Related Art
Following surgery, all patients experience some degree of discomfort associated with tissue dissection and removal of tissue during the surgery, at the operative site. Precise mechanisms involved in the production of pain are not fully understood. Pain management is largely composed of systemic administration of narcotics, either orally or parenterally, in the acute and convalescing postoperative state. Systemic administration can be accompanied by side effects, including nausea, vomiting, headache, dizziness, mental disturbance, sedation, constipation, respiratory depression and hypotension. Patient discomfort from pain and side effects of medication can impede patient mobilization, result in longer hospital stays and delay a person's return to normal activities such as employment.
In lumbar surgery, for example, pain arises from the skin incision, dissection and retraction of paraspinal musculature, removal of bony and ligamentous structures, and from direct trauma to the neural elements. Although the relative contribution of each of these is unknown, and might well vary, it is known that local measures such as local anaesthetic infiltration or epidural block, directed towards all of the mentioned structures can reduce postoperative pain.
Epidural administration of analgesics is a known method of pain control in various types of surgery: childbirth [Tan et al., 1994; Keller et al., 1995; Lowson et al., 1995]; major abdominal surgery (Dahl et al., 1992; Scott et al., 1995]; aortic repair [Slade, 1994]; thoracotomy [Lubenow et al., 1994; Bouchard et al. 1995; Thomson et al., 1995]; total knee and hip replacement [McBeath et al., 1995]; phantom pain [Miles, 1995]; and for palliation in patients with terminal cancer [Hicks et al., 1994].
A recent review states that since the first use of epidural opioids in 1979, there have been very few studies that properly compare epidural morphine with other administrative routes for the relief of postoperative pain [Cheam et al., 1994].
In a double-blind study, morphine (3 mg) alone, morphine (3 mg) and epinephrine, and saline (3 ml), respectively, were administered to three groups of patients undergoing lumbar laminectomy [Rechtine et al, 1984]. Medication was delivered into the epidural space as a single dose by catheter at completion of the laminectomy. Patients who received morphine went an average of 17 hours before requiring supplemental analgesics in comparison to those of the control (saline) group, who required supplemental analgesics after an average of seven hours. McGill Pain Scale scores, 24 hours after surgery, were also higher in control patients.
In another double-blind study, morphine (3 mg) and saline, respectively, were administered to two groups of patients undergoing laminectomy for disc herniation [Waikakul et al., 1992]. Medications were delivered as a single dose at completion of the surgical procedure. Patients who received morphine had a pain-free postoperative period averaging 6.3 hours compared to those of the control (saline) group, who had a pain-free postoperative period averaging 2.4 hours.
Morphine has been used in combination with methylprednisolone [McNeill et al., 1995]. In a randomized single-blind study, epidural administration of morphine (5 mg) and methylprednisolone (40 mg) significantly reduced the need for analgesia after decompression for spinal stenosis, but not after decompression for herniated disc. A single dose of medication was delivered to the epidural space through a catheter, which was removed at the completion of the surgical procedure.
Epidural administration of a combination of morphine (2 to 4 mg) and methylprednisolone (40 to 80 mg) has also been found to reduce the need for analgesia after lumbar decompressive surgery. Gelatin sponges were impregnated with the medications and the sponges were placed over the exposed dura in a laminotomy defect. The length of hospital stay was found to be less than historical controls. Earlier ambulation and reduced postoperative narcotic use was found for the study group.
The patent literature indicates an ongoing need in the area of operative and post-operative pain relief. For example, U.S. Pat. No. 5,458,631 (Xavier, Oct. 17, 1995) describes a pain relief method using an implantable catheter which includes four circumferential ring electrodes connected to terminals by fine wires embedded in the side wall of the catheter for attachment to a conventional electric pulse generator. A hollow body includes a lumen with a injection portal for continuously administering a pain-relieving agent in a liquid form. Japanese Patent Publication No. 6239746 (Okada, Aug. 30, 1994) apparently describes controlled-release coated morphine microcapsules for infusion into the subarachnoid space or epidural space. U.S. Pat. No. 5,227,165 (Domb et al., Jul. 13, 1993) describes lipospheres having an anaesthetic core and phospholipid coat for controlled, extended delivery of a pain relief agent. U.S. Pat. No. 5,124,155 (Reich, Jun. 23, 1992) describes a water swellable wound-healing dressing made up of fibronectin (or analogue thereof) in which can be dispersed various agents, including an analgesic, for delivery. The dressing can include collagens and other proteins. Russian Patent Publication No. 1477390 (Turko et al., May 7, 1989) apparently describes a treatment of osteochondrosis by removal of affect pulp from the disc and filling the cavity with a collagen sponge.